Coal Age

JUL 2015

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For many years, limestone-based rock dust has been the product of choice for North American coal mine explosion abatement. Typically, limestone products are readily available throughout North America and when processed to meet government speci- fications, adequately prevent the propaga- tion of a coal dust explosion. The old adage, "if it ain't broke, don't fix it," comes to mind when one thinks about business practices, especially in the ever- changing and increasingly more expensive coal mining industry. But, what if it's really broken and there is no fix? Even more impor- tantly, what if the issue puts lives at risk? After the Upper Big Branch explosion in West Virginia, the U.S. Mine Safety and Health Administration (MSHA) asked the National Institute for Occupational Safety and Health (NIOSH) to conduct an investigation into rock dust. The investi- gation revealed two significant concerns with the rock dust currently used in the U.S.; insufficient particles less than 200 mesh (75 microns) and the tendency to form a cake when wetted and dried that will not disperse. Needing a non-caking rock dust for the U.S. coal mining industry, NIOSH offered a grant to explore the development of a new solution. Imerys, one of the world's largest mineral producers with years of global min- eral expertise and a focus on innovation, won the grant bid to work alongside NIOSH to develop a new moisture-tolerant product to address the issue of caking rock dust. Research & Development After many meetings, extensive research, and lab testing, Imerys, with NIOSH assis- tance, developed a new modified rock dust that was produced in larger quantities for additional testing. The samples were tested for inerting effectiveness with a 20-L explosibility chamber. This was done by carefully mixing the new rock dust with pul- verized Pittsburgh No. 8 seam coal (77% less than 200 mesh) before being placed in the 20-L chamber for testing. The ratios of rock dust to coal varied and the results were compared to results of conventional rock dusts that are currently being used in coal mines (Table 1). The new modified rock dust performed as well as the current rock dusts in their ability to inert explosions. It was found that Imerys' new product showed greatly improved dispersibility over the current rock dusts being used in North American coal mines when subjected to wet and damp conditions. The new modified rock dust met or exceeded all the current government requirements (see Table 2), meaning that the new rock dust solution could begin to be used in North American mines without delay. The durability of Imerys' new rock dust was also evaluated alongside conventional July 2015 www.coalage.com 53 o p e r a t i n g i d e a s Moisture-tolerant Rock Dust Could Improve Safety Underground Imerys has developed a moisture-tolerant rock dust. Table 1 — Imerys Samples Tested in NIOSH 20-L Explosibility Chamber go = explosion ; no = no explosion, dnt = did not test; no-no = two tests conducted and both inerted the coal dust.

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